1. Field of the Invention
The present invention relates to an object detecting system for a vehicle, the object detecting system detecting an object such as a preceding vehicle by using an object detector such as a radar device.
2. Description of Related Art
When contamination such as mud or snow attaches to a transmitter/receiver section of a radar device, the object such as a preceding vehicle cannot be accurately detected, so that a system using the detection result cannot be properly operated. In order to solve this problem, Japanese Patent Publication No. 3428009 discloses an object detecting system, in which the threshold value of the reception level of the radar device is constructed by a first threshold value set to be lower than the reception level of the reflected wave from the road surface and a second threshold value which is set to be higher than the first threshold value so as to detect an object such as a preceding vehicle that should be detected; and when the reflected wave at the level exceeding the first threshold value is hardly received in a predetermined time, it is determined that contamination attaches to the transmitter/receiver section of the radar device to issue an alarm.
The reflected wave from a road surface, which is received by the radar device, changes in accordance with the kind of pavement, snowfall state, rainfall state and the like. For this reason, in the above-described conventional object detecting system, it is necessary to set the first threshold value corresponding to the condition of the road surface in order to enhance the determination accuracy of the contamination of the transmitter/receiver section of the radar device; and it is necessary to compare only the reflected wave in a predetermined beat frequency region corresponding to the reflected wave from a road surface with the first threshold value in order to distinguish the reflected wave from the road surface from those from the other objects. Therefore, there is a problem of complicated structure and operation.